The present invention related generally to the field of optical signal processing apparatus, and more specifically to an infrared crystalline spatial light modulator.
Two-dimensional spatial light modulators are devices which allow control of an optical wavefront for processing or imaging Operations. These devices, often referred to as light valves in the literature, have potential for application in large screen display systems as well as in optical data processing systems, including missile guidance and robotic vision systems. Listed below are several articles and patents which describe the construction and operation of various embodiments of such spatial light modulators.
1. "A Fast Silicon Photoconductor-Based Liquid Crystal Light Valve", P. O. Braatz, K. Chow, U. Efron, J. Grinberg and M. J. Little , IEEE International Electron Devices Meeting, pp 540-543, 1979. PA1 2. "LiNbO.sub.3 and LiTaO.sub.3 Microchannel Spatial Light Modulttors", C. Warde, A. M. Weiss and A.D. Fisher, SPIE Vol 218, Devices and Systems for Optical Signal Processing, 1980. PA1 3. "Applications of Priz Light Modulator", D. Casasent, F. Caimi, M. Petron and A. Khomenko, Applied Optics, Vol. 21., No. 21, November 1982, pp. 3846-3854. PA1 4. U.S. Pat. No. 3,517,206 entitled "APPARATUS AND METHOD FOR OPTICAL READ-OUT OF INTERNAL ELECTRIC FIELD", and incorporated herein by reference. PA1 5. U.S. Pat No. 3,823,998 entitled "LIGHT VALVE", and incorporated herein by reference. PA1 6. U.S. Pat. No. 4,618,217 entitled "ELECTRON BOMBARDED SILICON SPATIAL LIGHT MODULATOR", and incorporated herein by reference. PA1 7. U.S. Pat. No. 4,619,501 entitled "CHARGE ISOLATION IN A SPATIAL LIGHT MODULATOR", and incorporated herein by reference.
In certain spatial light modulators, spatially modulated data to be processed is imaged onto the face of an electro-optic crystal having a field-forming voltage thereacross. A spatially modulated charge distribution is formed across the face of the crystal, and when the opposed face of the crystal is illuminated with a uniform read light beam, the light emerging from the device is polarization modulated spatially with an amplitude of modulation that varies in accordance With the Original input data pattern. The charge distribution pattern may be formed on the face of the crystal by various means, as for example, by writing the pattern onto the crystal face with an electron source, or by the action of a laser beam on a suitable photoconductive layer deposited on the crystal face.
A spatial light modulator, for example, may specifically comprise a photosensitive semiconductor layer, such as a silicon photoconductor or photodiode layer, a light blocking layer, a dielectric mirror and an electro-optic crystal with a transparent electrode on its exposed face, arranged in a sandwich-like composite structure, and having a field-forming voltage applied thereacross. A control (write) illumination impinges on the face of the photoconductor while an output (read) illumination makes a double pass through the electro-optic crystal.
The silicon photoconductor responds to intensity variations in the control illumination impinging thereon. In the dark, most of the voltage applied across the composite structure appears across the photoconductor. The write beam, however, excites carriers in the silicon, which are driven by the internal field to the Si/electro-Optic crystal interface. The voltage across the silicon decreases, while the voltage across the electro-optic crystal increases. The read illumination passes through the electro-optic crystal, is reflected off of the dielectric mirror, and again passes through the electro-optic crystal before emerging from the device. Since the diffraction efficiency : a function of the voltage applied thereacross (which is a function of the intensity of the write illumination), optical control of the output read illumination is achieved.
In addition to the potential applications for spatial light modulators mentioned earlier herein, other applications exist for spatial light modulators which can modulate infrared radiation. For example, they may be useful as a processing component in an infrared optical systolic array processor, or as a display device to project infrared scenes, as in an infrared target simulator for testing infrared seekers.